The present invention relates to an above-grade multi-section cast concrete containment vessel which includes a primary liquid storage tank and intervening liquid and thermal liners, which collectively define primary, secondary and tertiary storage spaces, and, in particular, to an improved metal storage tank having a wall section or auxiliary flange plate which facilitates casting a cover to the tank to form a unitary assembly and mounting the tank to a base storage container.
A byproduct of society's increasing awareness to the environment and growing concerns over ground water contamination and the adverse effects of spilled petrochemicals (e.g. oil, gasoline etc.) has been the institution of varieties of regulatory controls. A predecessor containment tank to the present invention was developed to accommodate such regulations, especially for circumstances requiring above-grade storage of gasoline, and the containment of spills from accidental overfilling and tank ruptures. A further purpose was to accommodate concerns of the user to the cost and repair or replacement of portions of the containment system.
A variety of below-grade storage systems have been developed for containing pressurized and non-pressurized, flammable liquids, such as gasoline, propane or natural gas. Some of such containment vessels or tanks are shown at U.S. Pat. Nos. 1,958,487; 3,151, 416; 3,995,472; 4,183,221; 4,607,522; and 4,653,312. The foregoing vessels generally provide tank constructions which include a primary metal containment chamber that is surrounded by a reinforcing material, such as concrete. Intervening layers of thermal insulators and/or liquid impermeable materials are also disclosed in the various liquid storage assemblies.
Numerous above-grade storage vessels are also known. Most such vessels provide only a tank assembly having a single skin or layer of material, such as metal, concrete or fiberglass, which can be damaged and produce an uncontained spill.
To avoid spills, some tanks are diked behind a surrounding berm. Some tanks provide a multi-layered construction that includes a primary tank surrounded by a concrete or metal structure. The primary tank may or may not be integrated into the surrounding structure. U.S. Pat. Nos. 2,083,491; 2,136,390; 2,777,295; and 4,513,550 disclose cast concrete containment chambers wherein the structural walls include liquid impermeable liners.
Still other above-grade storage vessels are disclosed at U.S. Pat. Nos. 2,544,828; 3,562,977; 4,366,654; 4,372,906; 4,552,166; 4,826,644; 4,934,122; and 4,986,436. Various of the foregoing storage vessels provide a primary metal containment chamber which is surrounded by a monolithic cast concrete vault. One or more intervening membranes impermeable to a contained liquid are also provided.
Other diked metal storage tanks having secondary containment are shown at U.S. Pat. Nos. 4,895,272 and 5,346,093. Also disclosed at the tanks are an assemblies for directing spillage from the vent into a secondary storage space.
A principal deficiency of the foregoing above-grade storage containers is that the primary tank is exposed to a variety of physical dangers which can affect the life of the container. The sealed concrete tanks are also subject to potential cracking with the differential properties of thermal expansion and contraction of the materials; physical damage due to handling or collision from automobiles, trucks, on-site equipment or the like; and potential corrosion of reinforcement members within the concrete, such as from condensates which form between the steel liner and surrounding concrete assembly. Damage to any one of the container components typically requires replacement of the entire assembly.
In preference to a monolithic assembly, a modular assembly permits selective replacement of one or more of the container components in the event of damage or normal wear and tear to the individual components. A modular construction is also more accommodating of conventional manufacturing processes, such as are used to form open top septic tanks and detachable covers. Examples of a tank and a form used to cast tanks having integral covers and storage tanks which mount within a concrete base container are shown at U.S. Pat. Nos. 5,285,914 and 5,454,544.
Appreciating the latter secondary storage tanks are capable of storing volumes from 250 to 10,000 gallons, the physical sizes can produce difficulties in manufacture. A particular concern is the assurance of a proper alignment of the primary storage tank to the cover and ultimately the combined cover and tank to the base container. The casting form of the U.S. Pat. No. 5,454,544 patent assures proper alignment of the cover to the tank, however, the time and logistics to prepare the form and the necessity of having to own multiple forms for different sized tanks can be economically costly.
The present invention therefore provides an improved primary metal liquid storage container, which lends itself to conventional pre-cast concrete construction technology. The tank provides an improved construction with end walls which are shaped to align and center the tank within the base container. A flat top wall extends beyond roll formed or welded side and bottom wall panels and provides a platform or floor which supports the cover concrete during curing and which is cast into the cover. Fiberglass primary tanks can also be adapted to the invention. Tanks fitted with auxiliary casting flange plates are also shown which permits the use of the invention with conventional round steel and fiberglass tanks. Such tanks can be retrofit with an appropriate auxiliary flat flange to accommodate the casting in place of a cover that integrally includes the primary tank.